Noncatalytic reaction of isonitriles and carboxylic acids en route to amide-type linkages

We report the ligand enabled C(sp3)–H activation/olefination of free carboxylic acids in the γ-position. Through an intramolecular Michael-addition, δ-lactones are obtained as products. Two distinct ligand classes are identified that enable the challenging palladium-catalyzed activation of free carboxylic acids in the γ-position. The developed protocol features a wide range of acid substrates and olefin reaction partners and is shown to be applicable on a preparatively useful scale. Insights into the underlying reaction mechanism obtained through kinetic studies are reported.

Download Full-text

Reversing Reactivity: Stereoselective Desulfurative β-O-Glycosylation of Anomeric Thiosugars with Carboxylic Acids Under Copper or Cobalt Catalysis

10.26434/chemrxiv.11421576.v1 ◽

2019 ◽

Author(s):

Samir Messaoudi ◽

Nedjwa Bennai ◽

Amelie Chabrier ◽

Maha Fatthalla ◽

Expédite Yen-Pon ◽

...

Keyword(s):

Carboxylic Acids ◽

Late Stage ◽

Catalytic Amount ◽

Broad Scope ◽

Wide Range ◽

Glycosylation Reaction

We have discovered a new mode of reactivity of 1-thiosugars in the presence of Cu(II) or Co(II) for a stereoselective O-glycosylation reaction. The process involves the use of a catalytic amount of Cu(acac)2 or Co(acac)2 and Ag2CO3 as an oxidant in α,α,α-trifluorotoluene (TFT). Moreover, this protocol turned out to have a broad scope, allowing to prepare a wide range of com-plex substituted O-glycoside esters in good to excellent yields with an exclusive β-selectivity. The late-stage modification of phar-maceuticals by this method was also demonstrated.

Download Full-text

Generation of Phosphoranyl Radicals via Photoredox Catalysis Enables Voltage–Independent Activation of Strong C–O Bonds

10.26434/chemrxiv.6349253 ◽

2018 ◽

Author(s):

Erin Stache ◽

Alyssa B. Ertel ◽

Tomislav Rovis ◽

Abigail G. Doyle

Keyword(s):

Carboxylic Acids ◽

Functional Groups ◽

Single Step ◽

Direct Access ◽

Photoredox Catalysis ◽

Acyl Radical ◽

Synthetic Strategy ◽

Acyl Radicals ◽

Benzyl Radicals ◽

Aliphatic Carboxylic Acids

Alcohols and carboxylic acids are ubiquitous functional groups found in organic molecules that could serve as radical precursors, but C–O bonds remain difficult to activate. We report a synthetic strategy for direct access to both alkyl and acyl radicals from these ubiquitous functional groups via photoredox catalysis. This method exploits the unique reactivity of phosphoranyl radicals, generated from a polar/SET crossover between a phosphine radical cation and an oxygen centered nucleophile. We first show the desired reactivity in the reduction of benzylic alcohols to the corresponding benzyl radicals with terminal H-atom trapping to afford the deoxygenated product. Using the same method, we demonstrate access to synthetically versatile acyl radicals which enables the reduction of aromatic and aliphatic carboxylic acids to the corresponding aldehydes with exceptional chemoselectivity. This protocol also transforms carboxylic acids to heterocycles and cyclic ketones via intramolecular acyl radical cyclizations to forge new C–O, C–N and C–C bonds in a single step.

Download Full-text

Copper-Catalyzed Hydrocarboxylation of Allenes

10.26434/chemrxiv.7862456.v1 ◽

2019 ◽

Author(s):

Rémi blieck ◽

Marc Taillefer ◽

Florian Monnier

Keyword(s):

Carboxylic Acids ◽

Copper Catalysis ◽

Ligand Free ◽

First Time

The addition of carboxylic acids to allenes was performed for the first time with copper catalysis. The hydrocarboxylation reaction is totally regio- and stereoselective, ligand-free and used catalytic amounts of copper and base.

Download Full-text